(1) Field of the Invention
The present invention relates generally to a system and method for ultraviolet disinfection and, more particularly, to a system and method for ultraviolet disinfection of fluids.
(2) Description of the Prior Art
It is well known in the art to use ultraviolet light (UV) for the disinfection treatment of water. Ultraviolet light, at the germicidal wavelength of 253.7 nanometers, alters the genetic (DNA) material in cells so that bacteria, viruses, molds, algae and other microorganisms can no longer reproduce. The microorganisms are considered dead, and the risk of disease from them is eliminated. As the water flows past the UV lamps in UV disinfection systems, the microorganisms are exposed to a lethal dose of UV energy. UV dose is measured as the product of UV light intensity times the exposure time within the UV lamp array. Microbiologists have determined the effective dose of UV energy to be approximately about 34,000 microwatt-seconds/cm2 needed to destroy pathogens as well as indicator organisms found in wastewater. Typical prior art disinfection systems and devices emit UV light at approximately 254 nm, which penetrates the outer cell membrane of microorganisms, passes through the cell body, reaches the DNA and alters the genetic material of the microorganism, destroying it without chemicals by rendering it unable to reproduce.
Ultraviolet light is classified into three wavelength ranges: UV-C, from 200 nanometers (nm) to 280 nm; UV-B, from 280 nm to 315 nm; and UV-A, from 315 nm to 400 nm. Generally, UV light, and in particular, UV-C light is xe2x80x9cgermicidal,xe2x80x9d i.e., it deactivates the DNA of bacteria, viruses and other pathogens and thus destroys their ability to multiply and cause disease, effectively resulting in sterilization of the microorganisms. Specifically, UV xe2x80x9cCxe2x80x9d light causes damage to the nucleic acid of microorganisms by forming covalent bonds between certain adjacent bases in the DNA. The formation of these bonds prevents the DNA from being xe2x80x9cunzippedxe2x80x9d for replication, and the organism is unable to reproduce. In fact, when the organism tries to replicate, it dies. UV light with a wavelength of approximately between about 250 to about 260 nm provides the highest germicidal effectiveness. While susceptibility to UV light varies, exposure to UV energy for about 20 milliwatt-seconds/cm2 is adequate to deactivate 99 percent of the pathogens. Exposure to pathogens does not always cause disease, whether drinking contaminated water could produce disease depends on ingested and the health (nutritional and immunological) status of the person drinking the water. After studying certain variables, including the species and number of pathogens, the World Health Organization (WHO) has determined a standard of performance that must be met by acceptable water disinfection systems. The standard requires that an acceptable water disinfection system must be able to process contaminated water with 100,000 CFUs (colony forming units) of e-coli per 100 ml of water and produce outlet water with less than one CFU per 100 ml.
Generally, UV disinfection is a safe and reliable means for disinfecting drinking water for daily use, particularly given its relatively rapid, inexpensive, non-taste and odorless resultant treated water. UV light is a World Health Organization-approved method of disinfecting drinking water (Guidelines for Drinking Water Quality, vol. 1, World Health Organization, Geneva, Switzerland, 1993, p. 135). However, UV disinfection is not generally recommended for long-term storage of water.
Ultraviolet light has a proven track record of killing bacteria and viruses found in municipal wastewater. In addition, environmental concerns over the use of chemical disinfectants, coupled with improvements in ultraviolet-lighting technology, have led to the development of UV systems that treat spent metalworking fluids in the industrialized world; disinfect drinking water in developing countries; and clean aquaculture water, ballast water, and hospital air everywhere. Typically, chlorine gas or liquid is injected by a high-speed inductor directly into wastewater to kill bacteria before the water is discharged. According to industry experts, the main advantage of using UV instead of standard disinfection techniques is elimination of the transport and use of chlorine possible with the UV light-based system.
Used properly, ultraviolet light effectively destroys bacteria, viruses and other microorganisms in water and wastewater, without using chemicals. By doing away with chemical treatment, many other problems are also eliminated. There is no longer any need to worry about operator safety or the requirement for buildings for storage and handling of dangerous solutions and gases. Costly liability insurance premiums are significantly reduced. Testing of effluent for chlorine residual is no longer necessary, and toxicity problems associated with chlorine use are eliminated. Another factor leading municipalities to reconsider chlorination is its increased cost due to the national Uniform Fire Code adopted in 1993, which specifies expensive requirements for double containment of stored chlorine and chemical scrubbers in case of leaks.
Prior art applications of UV light used for disinfection of water include private drinking water supplies, municipal drinking water treatment plants, industrial product and process waters, and commercial applications, and wastewater treatment in primary, secondary, and tertiary treatment process for industrial, commercial and municipal wastewater treatment applications.
While UV purification is well suited for many residential, commercial, industrial and municipal water and wastewater treatment applications, considerations of the water quality and about the desired or required effluent purity impact the system design and performance. Prior art UV disinfectant systems work best when the water temperature is between about 35 and about 110 degrees Fahrenheit, since extreme cold or heat will interfere with the UV system performance.
The UV light source used in prior art are typically low pressure mercury lamps, which can effectively clean water of dangerous and illness-causing viruses and bacteria, including intestinal protozoa such as Cryptosporidium, Giardia, and E.coli, provided that the proper number and configuration of lamps are included in the system. All known prior art systems calculate, design and configure the proper number and arrangement or positioning of lamps as set forth and described by formulas developed and published by Dr. George Tchobanoglous, presently of University of California at Davis.
Dr. George Tchobanoglous, professor emeritus of civil and environmental engineering at the University of California, Davis and former chairperson on a committee of academic, industrial, and environmental consultants who drafted guidelines on UV disinfection for California in 1994, is perhaps the leading authority on UV water disinfectant systems and methods used in the prior art. His formulas for predicting the minimum required number of UV lamps and configuration of same are based on a key component of positioning the UV lamps within the water to be treated, and more particularly, requiring a lamp centerline-to-centerline distance of not more than three (3) inches to ensure effective disinfectant UV dosage for any influent system and flow rate; these formulas referred to as xe2x80x9cpoint source summationxe2x80x9d.
Traditional low-pressure UV systems found in the prior art are used for low flow water disinfection or smaller projects with air and surface applications. The low pressure UV lamp treats between 10 and 180 gallons per minute of fluid using up to 12 lamps at a time. As flows increase or higher UV doses are required, the multiple low-pressure lamp concept becomes complex and cumbersome. The medium pressure UV lamp offers a solution to maintain simplicity and cost effectiveness in meeting the higher flow and higher dose challenge. A single medium pressure UV lamp can treat up to 2,300 gallons per minute of fluid. Notably, the UV disinfection systems and methods used by prior art consistently involve and teach the use of low pressure UV lamp and equipment for water, air and surface disinfection applications. These prior art systems require treatment chambers, usually constructed of stainless steel. The prior art air systems also use low-pressure UV lamps and treat air in storage tanks.
Where the prior art uses a medium pressure UV lamp, typically single lamp units are used, possibly capable of treating 10 to 2,300 gallons per minute of fluid. In these cases, prior art requires special enhanced medium pressure UV lamps, with these applications restricted for use treating high and low temperature fluids that are unachievable with low-pressure lamps. Even with such configurations, the use of immersion-positioned UV lamps in an effective chamber design still requires system downtime to change the UV lamp. Special enhanced UV lamp design is required to achieve the highest performance in TOC reduction, ozone removal and chlorine destruction.
Problems exist for prior art systems where factors are present that inhibit UV light from penetrating the water. Turbidity, which is the state of water when it is cloudy from having sediment stirred up, interferes with the transmission of UV energy and decreases the disinfection efficiency of the UV light disinfection system. In cases where the water has high iron or manganese content, is clouded and/or has organic impurities, it is usually necessary to pre-treat the water before it enters the UV disinfection stage because deposits on the quartz-encased UV lamps, which are immersed in the water to be treated, interfere with the UV light transmission, thereby reducing the UV dose and rendering the system ineffective. Prior art typically employs UV purification in conjunction with carbon filtration, reverse osmosis and with certain chemicals to reduce fouling between cleanings of the quartz sleeves that surround the UV lamps.
Typically, prior art devices and systems for disinfecting water via ultraviolet light exposure commonly employ standard ultraviolet light sources or lamps encased in quartz sleeves and suspended in the water being treated. Benefits of using ultraviolet light for disinfecting water, particularly waste water treatment, include the following: no chemicals, like chlorine, are needed to ensure effective water disinfection provided that the proper number of lamps are used and properly positioned for a given influent and flow rate; since no chemicals are required in the disinfection process, no storage and/or handling of toxic chemicals is required; no heating or cooling is required to ensure disinfection; no storage tanks or ponds are necessary because the water can be treated as it flows through the system; no water is wasted in the process; no change in pH, chemical or resistivity of the water being treated; approximately at least 99.99% of all waterborne bacteria and viruses are killed via UV light exposure for disinfection; thereby providing increased safety of using the system and effectiveness of same.
As set forth in the foregoing, prior art UV water treatment systems disinfect and remove microorganisms and other substances from untreated, contaminated water sources and produce clean, safe drinking water. The core technology employed in WaterHealth International""s system is includes a patented, non-submerged UV light. This technology is claimed by WHI to be a recent and tested innovation developed at the Lawrence Berkeley National Laboratory, a premier, internationally respected laboratory of the U.S. Department of Energy managed by the University of California. This prior art system delivers a UV dose of up to 120 mJ/cm2, which is more than three times the NSF International requirement of 38 mJ/cm2 and exceeds World Health Organization and EPA water quality standards and effectively treats bacteria, viruses and Cryptosporidium in drinking water. In addition, recent research conducted at two different laboratories indicates that UV doses of 10 mJ/cm2 or less produce 4-log reductions in Giardia. Based on this research, UV dosage of up to 120 mJ/cm2 greatly exceeds the dosage required for inactivation of Giardia. Additional components included in WaterHealth International""s systems effectively treat specific problems such as turbidity, silt, tastes, odors and various chemicals. Significantly, WHI""s systems are not intended to treat raw sewage or wastewater.
Among applications for UV disinfection systems for water include the beverage industry, wastewater treatment, and surface treatment. By way of example and explanation, ot filled beverages, cold filled beer and other sensitive drinks are susceptible to contaminants introduced by the liners of closures. Mold is of particular concern since packaging headspace frequently contains low levels of oxygen. Medium pressure UV inactivates mold spores to prevent this problem, including contamination of beverages during production and storage, which can cause discoloration, unusual taste or bad flavor, and reduced shelf life. UV disinfection systems solve these issues by eliminating problem microorganisms without adding chemicals or heat disinfection of municipal wastewater using UV light avoids problems associated with storage, transport and use of chemicals and associated regulation for them. UV disinfection is safe, cost effective and applicable to tertiary treated effluent as well as secondary, primary, and combined sewer overflows (CSO) and storm water. Ultraviolet light can help improve shelf life of products and allow processors to reduce chemical additives in wash water without sacrificing high levels of disinfection. UV light provides non-chemical microbial control for captive water loops without altering the taste, color or odor of the food. Environmentally safe UV disinfection is one of the few water treatment methods unburdened by regulatory restrictions, consumer/environmental group concerns or high operation costs. Packaging surface UV systems also increase product quality and shelf life by reducing contamination. Applications include plastic containers, cups, caps, films, foils and extended shelf life filling machines.
By way of comparison between prior art UV disinfection systems and traditional chlorine-based disinfection, the commercially available Trojan UV system can disinfect more consistently and effectively than is possible with current chlorination procedures, with significantly less cost per gallon. The UV treatment takes approximately 6-10 seconds in a flow-through channel, while chlorine requires 15-20 minutes treatment time in a contact tank. According to Trojan literature, UV disinfection can greatly reduce capital and operating costs. With UV treatment, it is possible to eliminate the need for large contact tanks designed to hold peak flows. Space requirements are reduced and no buildings are needed since the entire process and related commercially available equipment are designed to operate outdoors. Refer to the table below for side-by-side qualitative comparison of UV disinfection versus chlorine- and ozone-based systems and methods.
However, cleaning and maintenance of the quartz sleeves, which are necessary and essential to protect the UV lamp or light source used in nearly all prior art systems, can become a time-consuming duty, especially when working with multi-lamp low pressure systems. During operation while the UV lamps and quartz sleeves are suspending in the water to be treated, minerals and contaminants in the water deposit onto the quartz sleeves, thereby causing fouling on the sleeve surface. This fouling reduces the effectiveness of the UV lamps because the fouling interferes with the UV light transmission into the water. To save time and prevent quartz sleeve fouling a cleaning mechanism can be supplied for either manual or automatic operation, like using wiper glides over the sleeves to remove deposits, which may block the light emitted from the UV lamp. This provides improved performance and reduces maintenance time, but only where the water quality is low. In every case, the UV lamps encased in quartz sleeves must be removed for cleaning on at least a monthly basis, depending on specifics of a given system and its influent and flow rates. The cleaning requires the system to be shut down temporarily or diverted to other UV lamps, so system shut down decreases capacity and/or increases operating costs. Furthermore, the quartz sleeve-encased lamps are extremely heavy, requiring the use of a crane to raise them out of the water flow stream for cleaning. Cranes and crane time are expensive, thereby increasing overall system costs. Only one company, WaterHealth, Inc., might in any way suggest the use of non-submerged lamps for UV systems but these are limited expressly in advertising literature as applicable only and exclusively in applications that do not require high purification, e.g., previously purified drinking water but not wastewater treatment.
Thus, there remains a need for a UV disinfection system for treating fluids having reduced maintenance time and costs, increased flow rates for a given disinfection level, and overall lower equipment, installation, and system costs.
The present invention is directed to a UV disinfection system and method for treating fluids, particularly water, whereby the UV light source requires less maintenance and cost than prior art systems and devices while providing at least the same disinfection level for a given influent and flow rate thereof.
In a preferred embodiment, a UV disinfection system for treating fluids is configured and arranged to function effectively with at least one UV light source or lamp that is not submerged in the fluid to be disinfected. The UV light source is positioned outside the fluid to be disinfected via exposure to at least one UV dose zone wherein UV light is projected into the zone.
The UV light source may be presented in at least two primary configurations; a vertical riser configuration and a planar or horizontal configuration. In the vertical riser configuration the UV light source is positioned above the fluid to be treated and projecting a UV dose zone downward toward and into the fluid to be treated, with the fluid moving upward toward the UV light source. Alternatively, the UV light source may be presented in a planar or horizontal design, wherein the UV light source is positioned above the fluid to be treated and projecting a UV dose zone downward toward and into the fluid to be treated, with the fluid moving in a direction substantially perpendicular to the UV dose zone.
Preferably, the UV dose zone includes at least one zone, more preferably three zones, wherein one zone includes a surface zone of an interface plate positioned between the UV light source and the fluid to be treated.
The present invention is further directed to a method for treating fluids by disinfecting those fluids using UV light projected by at least one IN light source producing at least one dose zone, the UV light source being positioned outside the fluid.
Thus, the present invention provides a UV disinfection system for treating fluids having reduced maintenance time and costs, increased flow rates for a given disinfection level, and overall lower equipment, installation, and system costs.
Accordingly, one aspect of the present invention is to provide a system and method for disinfecting fluid including at least one UV light source positioned outside the fluid to be treated with the at least one UV light source producing at least one UV dose zone for disinfecting the fluid.
Another aspect of the present invention is to provide a system and method for disinfecting fluid including at least one UV light source positioned outside the fluid to be treated with the at least one UV light source producing three UV dose zones for disinfecting the fluid, with one UV dose zone provided at a surface zone of an interface plate positioned between the UV light source and the fluid to be treated.
Still another aspect of the present invention is to provide a system and method for disinfecting fluid including at least one UV light source positioned outside the fluid to be treated with the at least one UV light source producing at least one UV dose zone for disinfecting the fluid, wherein the at least one UV light source is a medium-to-high intensity UV light source.
These and other aspects of the present invention will become apparent to those skilled in the art after a reading of the following description of the preferred embodiment when considered with the drawings.